This invention relates to printing machines, and more particularly, to apparatus for collecting and storing particulate material prior to disposal thereof. The apparatus is especially useful for use with toner particles removed from the charge-retentive surfaces of printing machines such as those employing the well known xerographic imaging process.
In the art of xerography or other similar image reproducing arts, a latent electrostatic image is formed on a charge-retentive surface such as a photoconductor which generally comprises a photoconductive insulating material adhered to a conductive backing. The photoconductor is first provided with a uniform charge after which it is exposed to a light image or an original document to be reproduced. The latent electrostatic images, thus formed, are rendered visible by applying any one of numerous pigmented resins specifically designed for this purpose. In the case of a reusable photoconductive surface, the pigmented resin, more commonly referred to as toner which forms the visible images is transferred to plain paper.
It should be understood that for the purpose of the present invention, which relates to the removal and collection of residual toner particles, the latent electrostatic image may be formed by means other than by the exposure of an electrostatically charged photosensitive member to a light image of an original document. For example, the latent electrostatic image may be generated from imformation electronically stored or generated, and the digital information may be converted to alphanumeric images by image generation electronics and optics. However, such image generation electronic and optic devices form no part of the present invention.
Although a preponderance of the toner forming the images is transferred to the paper during transfer, some residual toner (which also contains debris) remains on the photoconductive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. It is essential for continued optimum operation that the toner remaining on the surface be thoroughly cleaned therefrom.
A commercially successful mode of cleaning employed in automatic xerography utilizes a brush with soft bristles which have suitable triboelectric properties. While the bristles are soft they are sufficiently firm to effect removal of residual toner particles from the charge-retentive surface.
In addition, webs, belts and blades are known to be useful in cleaning such surfaces, blades being one of the most commonly used toner removal devices in the smaller and slower speed machines commercially available today.
Regardless of how the toner particles are removed from the charge-retentive surface they are either recirculated to the developer housing for reuse or discarded. When the toner particles are reused they are first separated from the debris mixed therewith. The present invention, as mentioned above, is directed to apparatus for collecting the residual toner and then discarding it. Typically the toner removed from the surface is augered to either the front or the rear of the machine to be deposited into a receptacle which is used for temporarily storing the particles and for subsequently removing them from the machine.
By far, the most common receptacle utilized for the foregoing purposes is in the form of a bottle into which the toner particles are simply allowed to fall until the bottle is full (i.e. contains all the toner it is capable of handling). This method of collecting the toner particles is somewhat inefficient because the full capacity of the bottle can not be used. This is because the toner first falls to the bottom of the bottle and then builds up in christmas tree fashion until the apex of the tree reaches the mouth of the bottle at the top thereof. As will be appreciated with such an arrangement there are voids between the vertical walls of the bottle and the toner mass forming the christmas tree shape. Thus, all of the bottle capacity is not utilized. Additionally since the packing of the toner in the bottle relies solely on gravity rather than a positive packing method the density to which the toner is packed further diminishes the capacity of toner collection.
Another, less common mode of collecting toner particles, comprises, as shown in U.S. Pat. No. 3,927,937, a storage chamber into which toner particles are moved into the chamber. The chamber forms a part of a cleaning assembly which assembly must be removed in order to discard the particles collected in the chamber without contaminating other parts of the machine in which it is used. While it was most likely intended by the patentee to utilize available space that had not before been possible with prior art devices, such utilization is limited because of the increasing forces required to continue to pile the particles higher and higher above the entrance point for the particles.
Still another apparatus for removing and collecting toner is disclosed in patent application Ser. No. 623,609, filed in the United States Patent and Trademark Office on June 22, 1984. The invention disclosed in the foregoing application is assigned to the same assignee as the invention disclosed herein. As disclosed therein, an auger structure having a single auger segment is employed for conveying toner into a bottle through an opening in a vertical wall thereof. Anti-bridging devices have been found to be necessary in toner removal systems utilizing augers. This is because the toner tends to cake or agglomerate in the pitches or flights of the auger resulting in inefficient handling of the toner. In the absence of anti bridging devices, toner delivery rates in excess of disposal rates, result in bridging in the delivery area. Flow is blocked and the system fails.
Tapping on the side of the toner collecting housing is known to be a viable option to solving the problem of toner caking or packing in the auger. Electromechanical vibrators or solenoids fastened to the toner collector housing function satisfactorily but are too costly.
An apparatus for collecting toner particles and filling a receptacle to capacity with minimal toner bridging is obviously a most desirable invention, particularly if it can be accomplished without appreciably increasing the cost of the removal and collection system.